In moderate to heavy rain with the toyota dynamic cruise control engaged on the highway between 55 and 70 mph, the prius has dangerously accelerated itself towards a car immediately in front of my car and would have created a front-to-rear collision if i was not extremely vigilant and manually braked and canceled the adaptive cruise system within 10-20 feet of the car in front of me. the system seems to operate blindly in moderate to heavy rain and will accelerate to user-set speed even when a car is traveling slower immediately in front of my vehicle. i strongly suspect the pre-collision braking is failing at the same time as the dynamic cruise (in rain) since it relies on the same components. the prius prime needs to be reprogrammed to not allow dynamic cruise engagement in moderate to heavy rain. this is a very dangerous situation because driver visibility is already impaired under these conditions. if this did not occur multiple times, i would not have believed it was actually happening. the prius manual says that rain can cause the system to not behave as intended; however, in that case it needs to be automatically disabled so it does not create a very false sense of security. this is going to cost lives if it's not reprogrammed. i would be surprised if this was the only toyota that exhibits this dangerous behavior. i strongly believe that lives can be saved with a simple reprogram of the system to not allow operation under conditions that can create unintended acceleration into a slower moving vehicle. toyota should save themselves millions in potential liability and take this suggestion seriously.